Propeller thrust transmission device for a watercraft propulsion device

ABSTRACT

A propeller thrust transmission device for a watercraft propulsion device prevents an occurrence of a precession of a spacer on an entire circumference around a taper part if a water resistance force acts upward on a propeller. The propeller thrust transmission device includes a taper part of an outer shaft part of a propeller shaft that is fitted in a spacer divided into a first half and a second half. A thrust force acting on a propeller is received by the taper part of the propeller shaft via the spacer. The first half includes a taper hole whose surface is contra-positive to the taper part and in which the taper part is fitted. The second half has apart extending from one side of a ring-shaped wall part close to the propeller, which is a small diameter tube part for being fitted in a hole of an attachment part having a space S to the propeller shaft, and a part extending from the other side of the ring-shaped wall part, which is a large diameter tube part for being fitted in a outer peripheral surface positioned outside the taper hole of the first half.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a propeller thrust transmission devicefor a watercraft propulsion device, which is a part for transmitting athrust force acting on a propeller to a propeller shaft, as thepropeller in an outboard motor or an inboard/outboard motor rotates.

2. Description of the Related Art

Conventionally, a propeller thrust transmission device, which is a partfor transmitting a thrust force acting on a propeller to a propellershaft, as the propeller in a watercraft propulsion device rotates,includes a taper part and a spacer of the propeller shaft. Oneconventional propeller thrust transmission device of an exhaust devicefor an outboard motor and the like is disclosed in FIG. 2 of JP-B-Sho62-15399.

FIG. 4 of the present application is an enlarged cross sectional viewfor showing a propeller thrust transmission device for a watercraftpropulsion device that is practically equivalent to the propeller thrusttransmission device shown in FIG. 2 of JP-B-Sho 62-15399. The propellerthrust transmission device has the following structure. An attachmentpart 14 of a propeller 13 is fitted in and fixed to an outer shaft part11 a protruding outward from a gear case 12 of a propeller shaft 11. Thepropeller thrust transmission device includes a taper part 11 b at apart close to the gear case such that a diameter of an end close to thegear case is large and a diameter of an end close to the propeller issmall, and a spacer 16 in which the taper part 11 b is fitted. Thisattachment part 14 is structured with a boss 14 a united with animpeller part of the propeller and having an exhaust passage for lettingcombustion gas of an engine through, a tube-shaped rubber damper 14 bpress-fitted in the boss 14 a, a bush 14 c press-fitted inside therubber damper 14 b, and an end plate 14 d. The attachment part 14 isfixed by a nut 15. The spacer 16 is shaped to have a taper hole 16 awhose surface is contra-positive to the taper part 11 b and in which thetaper part 11 b is fitted, an end surface 16 b touching a side end wall14 a′ of the boss 14 a, and a small diameter tube part 16 c fitted in ahole 14 a″ formed in the side end wall 14 a′. In this propeller thrusttransmission device, the taper part 11 a of the propeller shaft 11receives a thrust force acting on the propeller 13 via the spacer 16 asthe propeller 13 rotates in a normal direction.

However, in the propeller thrust transmission device for a watercraftpropulsion device shown in FIG. 4, when a watercraft propels at a highspeed (when the propeller rotates at high speed), a hull or a sterncomes to the surface, a draft line lowers, an upper part of thepropeller is exposed to the air, and a water resistance force F actsupward on a lower part of the propeller 13. In such a situation, thiswater resistance force F is transmitted from the attachment part 14 ofthe propeller 13 to the small diameter tube part 16 c of the spacer 16.A point on the small diameter tube part 16 c of the spacer 16 to which awater resistance force is transmitted has is spaced by a distance S fromthe propeller shaft 11 and is distant from a point of application of anaverage thrust on a thrust force transmission surface between the taperhole 16 a of the spacer 16 and the taper part 11 b united with it. Thus,a moment effect occurs on a lower part of the taper part 11 b of thepropeller shaft 11 rotating at a high speed due to the water resistanceforce F and the distance L. This situation causes a precession being aload fluctuation in which a surface of the taper hole 16 a of the spacer16 repeatedly comes off and firmly contacts the taper part 11 b of thepropeller shaft 11, which results in the spacer 16 abrading the thrusttransmission surface (the taper part 11 b). Further, the concentricitybetween the boss 14 a and the bush 14 c are retained via the rubberdamper 14 b, and thus when the watercraft propels at a high speed (whenthe propeller rotates at a high speed), the hull or the stern comes tothe surface, a draft line lowers, an upper part of the propeller isexposed to the air, and a water resistance force F acts upward on thelower part of the propeller 13. In such a situation, a lower part of therubber damper 14 b is compressed, and as a result, the boss 14 a movesup toward the bush 14 c. Therefore, the side end wall 14 a′ of the boss14 a slides on the end surface 16 b. The side end wall 14 a′ of the boss14 a continuously slides on the end surface 16 b of the spacer 16 andthis slide movement causes an abrasion on both the sliding surfaces dueto rotations of the propeller 13 if there is a water resistance force Facting thereupon. Because of an abrasion of the sliding surfacesprogressing, the side end wall 14 a′ of the boss 14 a and the endsurface 16 b of the spacer 16 separate below the propeller shaft 11 andcontact above the propeller shaft 11. Therefore, because the propeller13 is rotating, the rotation accompanies contacts around the concernedparts. This results in large intensification of the precession mentionedabove and an occurrence of abrasion on the thrust transmission surface(the taper part 11 b) by the spacer 16.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a propeller thrust transmission devicefor a watercraft propulsion device in which a moment effect issubstantially avoided even if a water resistance force acts upward on alower part of a propeller when an upper part of the propeller is exposedin the air as the propeller rotates, thereby an occurrence of aprecession by a spacer around an entire circumference of a taper part ofa propeller shaft is prevented, and abrasion by a spacer on a thrusttransmission surface is prevented.

A first aspect of preferred embodiments of the present inventionprovides a taper part provided at a position close to a gear case on anouter shaft part, in which a propeller attachment part is fitted in andfixed at the outer shaft part protruding outward from the gear case of apropeller shaft, a diameter of an end of the taper part located close tothe gear case is large and a diameter of an end of the taper partlocated close to a propeller is small, and a spacer including a taperhole whose surface is contra-positive to the taper part and in which thetaper part is fitted, the spacer including an end surface arranged tocontact a side end wall of the propeller attachment part, a smalldiameter tube part fitted in a hole formed in the side end wall of thepropeller attachment part such that a thrust force acting on thepropeller when the propeller rotates in its normal direction is receivedby the taper part of the propeller shaft via the spacer, a first halfand a second half separate from the first half, wherein the first halfincludes the taper hole whose surface is contra-positive to the taperpart and in which the taper part is fitted, the second half is locatedcloser to the propeller relative to the first half and has a ring-shapedwall part firmly contacting a side surface of the first half, a partextending from one side of the ring-shaped wall part close to thepropeller is the small diameter tube part fitted in the hole formed inthe side end wall of the propeller attachment part and spaced from thepropeller shaft, and a part extending from the other side of thering-shaped wall part has a large diameter tube part fitted in an outerperipheral surface positioned outside the taper hole.

A second aspect of preferred embodiments of the present inventionprovides the propeller thrust transmission device for a watercraftpropulsion device in accordance with the first aspect, in which a firmcontacting surface between the side surface of the first half and thering-shaped wall part of the second half corresponds to a small diameterend of the taper part of the propeller shaft.

A third aspect of preferred embodiments of the present inventionprovides the propeller thrust transmission device for a watercraftpropulsion device in accordance with the first or second aspect, inwhich the small diameter tube part is forcedly fitted in the hole formedin the side end wall of the propeller attachment part.

A fourth aspect of preferred embodiments of the present inventionprovides the propeller thrust transmission device for a watercraftpropulsion device in accordance with any one of the first through thirdaspects, in which the propeller attachment part is furnished with a bossunited with an impeller part of the propeller, a bush mounted inside theboss in which the propeller shaft is fitted, an elastically deformabledamper member provided between the boss and the bush, and aconcentricity retaining ring provided on an end part of the bush closeto the gear case so as to fill a space between the bush and the boss andso as to retain the concentricity between the bush and the boss, and isfixed to the propeller shaft by a nut.

In accordance with the first aspect of preferred embodiments of thepresent invention, when a hull or stern comes to the surface and anupper part of the propeller is exposed to the air when the propellerrotates, a water resistance force acts upward on a lower part of thepropeller. This water resistance force acting upward on the lower partof the propeller becomes maximum together with a thrust force when thewatercraft propels at a high speed, and acts on the propeller shaft. Awater resistance force acting upward on the lower part of the propelleris transmitted from the attachment part of the propeller to the smalldiameter tube part of the second half. Further, the force is transmittedfrom the large diameter tube part of the second half to the first half.At this point, if the spacer is formed into one body as in aconventional case described above, a moment occurs due to an upwardforce acting upward on the small diameter tube part at a point ofapplication of an average thrust on a thrust force transmission surface.However, in preferred embodiments of the present invention, the spaceris separated into the first half and the second half. A fitting betweenthe large diameter tube part of the second half and the outer peripheralsurface positioned outside the taper hole of the first half is notactually integrated into one unitary body. Therefore, a water resistanceforce acting upward on the lower part of the propeller acts upward onthe small diameter tube part of the second half, and is transmitted fromthe large diameter tube part to the outer peripheral surface positionedoutside the taper hole because of the space between the small diametertube part and the propeller shaft. Consequently, a water resistanceforce acts on a position practically corresponding to a point ofapplication of an average thrust on a thrust force transmission surfacebetween the taper hole of the first half and the taper part of thepropeller shaft, and thus a moment effect almost does not occur. Anoccurrence of a precession of a surface of the taper hole of the spaceraround an entire circumference of the taper part of the propeller shaftis prevented, and thus an abrasion on a thrust transmission surface bythe spacer can be prevented. Further, a position in which an upwardforce acting on the propeller is transmitted to the propeller shaft ischanged because the spacer is divided into the first part and the secondpart. Therefore, a reshaping of the propeller or the gear case is notnecessary, and an application to a product that has been already shippedand sold can be facilitated.

In accordance with the second aspect of preferred embodiments of thepresent invention, a ring-shaped side wall of a second half can beformed to have a thickness with a minimum necessary strength. Thisallows the taper hole of the first half to be contra-positive to asurface of the taper part of the propeller shaft over an entire lengthof the taper part, and thereby an occurrence of a moment effect isinhibited. A thrust force per unit area becomes smaller because an areareceiving a thrust force becomes larger than a conventional case, and aforce acting upward on the propeller per unit area becomes small also.Therefore, it can more effectively prevent an occurrence of a precessionof the surface of the taper hole of the spacer around the entirecircumference of the taper part.

In accordance with the third aspect of preferred embodiments of thepresent invention, an assemblage from the first half, the second halfand the propeller into a securely fixed state is facilitated. Anoccurrence of a precession can be prevented on a fitting surface betweenthe first half and the second half, and a fitting surface between thesecond half and the attachment part of the propeller, and thereby anabrasion can be prevented.

In accordance with the fourth aspect of preferred embodiments of thepresent invention, the boss and the bush retain concentricity about adirection of the propeller shaft. The concentricity is retainedgenerally via the elastically deformable damper member provided betweenthe boss and the bush, and via the concentricity retaining ring at apart close to the gear case. When a watercraft propels at a high speed(when the propeller rotates at a high speed), a hull or a stern comes tothe surface, a draft line lowers, an upper part of the propeller isexposed to the air. A water resistance force acts upward on a lower partof the propeller, and compresses a lower part of the rubber damper.Therefore, a state that the bush moves up toward the boss is preventedin a part close to the gear case if the bush itself moves up toward theboss. As a result, a slide movement of the side end wall of the boss onthe end surface of the spacer is prevented, and thus occurrences of anabrasion on the side end wall of the boss and the end surface areprevented. Therefore, an occurrence of an abrasion on the thrusttransmission surface (the taper part) by the spacer is prevented.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a watercraft propulsion device according to afirst preferred embodiment of the present invention.

FIG. 2 is a cross sectional view of a propeller thrust transmissiondevice for a watercraft propulsion device according to the firstpreferred embodiment of the present invention.

FIG. 3 is a cross sectional view of a propeller thrust transmissiondevice for a watercraft propulsion device according to a secondpreferred embodiment of the present invention.

FIG. 4 is a cross sectional view of a conventional propeller thrusttransmission device for a watercraft propulsion device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinafter.

As shown in FIG. 1, an outboard motor 21 as the “watercraft propulsiondevice” is mounted on a transom board 20 a at a stern of a hull 20 via aswivel bracket 22 such that the outboard motor 21 can be tilted up. Apropeller thrust transmission device according to a preferred embodimentof the present invention is provided for a propeller shaft 30 and apropeller 31 of the outboard motor 21.

First, a general construction of the outboard motor 21 will bedescribed. As shown in FIG. 1, the outboard motor 21 has a top cowl 23,a bottom cowl 24, an upper case 25, and a lower case (gear case) 26. Anengine 27 is disposed inside the top cowl 23 and the bottom cowl 24. Thepropeller 31 is driven by a rotation output of the engine 27 via a driveshaft 28 disposed vertically inside the upper case 25, a gear shaft 29disposed vertically and the propeller shaft 30 disposed horizontally inthe lower case 26.

The upper end of the drive shaft 28 is connected with a crankshaft ofthe engine 27 such that they are rotatable together. A lower end of thedrive shaft 28 is connected with the gear shaft 29 such that they arerotatable together. A bevel gear 43 fixed at the lower end of the gearshaft 29 is in meshing engagement with bevel gears 44 and 45 rotatablysupported by the lower case 26. Rotation of the drive shaft 28 istransmitted to the gear shaft 29 with the rotational speed slowed down,and a rotational direction of the propeller shaft 30 is changed by anactuation of a dog clutch 46 in the transmission.

The dog clutch 46 is provided in a location close to the front end ofthe propeller shaft 30 to be movable axially therealong. When the dogclutch is in a neutral position, a protrusion of the clutch is releasedfrom engagement with either bevel gear 44 or 45, and rotation of thepropeller shaft 30 stops.

When the dog clutch 46 moves closer to the propeller 31, the protrusionof the clutch engages with the bevel gear 44, and the propeller shaftrotates in a direction to drive the watercraft forward. When the dogclutch 46 moves closer to the hull, the protrusion of the clutch engageswith the bevel gear 35, and the propeller shaft 30 rotates in adirection to drive the watercraft rearward.

As shown in FIG. 2, the propeller shaft 30 is almost horizontallydisposed and rotatably supported in the lower case 26. An attachmentpart 32 of the propeller 31 is fixed to a part close to the rear end ofthe propeller shaft 30. The attachment part 32 is structured with a boss33 united with the propeller 31, a tubular rubber damper 34 as the“damper member” press-fitted in the boss 33, a bush 35 press-fittedinside the rubber damper 34, and an endplate 36 loosely fitted to thepropeller shaft 30 and fitted in the boss 33 with a loose fit tolerance.The bush 35 is spline-fitted on an outer shaft part 30 a protrudedoutward from the gear case 26 of the propeller shaft 30 while the boss33, the rubber damper 34 and the bush 35 are combined together. Theendplate 36 is fitted in the boss 33 and fixed thereto by a nut 38.Although the rubber damper 34 in this preferred embodiment is preferablymade of rubber, the “damper member” can be formed with an elastic memberother than rubber that can be formed into a tubular shape andelastically deforms between the boss 33 and the bush 35.

The propeller thrust transmission device is furnished in the watercraftpropulsion device with the above construction as described hereinafter.

In the propeller thrust transmission device for a watercraft propulsiondevice, as mentioned above, the attachment part 32 of the propeller 31is spline-fitted on the outer shaft part 30 a protruding outward fromthe gear case 26 of the propeller shaft 30, and fixed thereto by a nut38. The propeller thrust transmission device includes a taper part 30 bin a position close to the gear case of the outer shaft part 30 a, inwhich a diameter of an end close to the gear case is larger and adiameter of an end close to the propeller is smaller, and a spacer 40whose surface is contra-positive to the taper part 30 b and in which thetaper part 30 b is fitted. A thrust force acting on the propeller 31when the propeller 31 rotates in its normal direction is received by thetaper part 30 b of the propeller shaft 30 via the spacer 40.

The spacer 40 preferably includes a first half 41 and a second half 42.The first half 41 includes a taper hole 41 a whose surface iscontra-positive to the taper part 30 b of the propeller shaft 30 and inwhich the taper part 30 b is fitted. The second half 42 is provided at apart close to the propeller relative to the first half 41 and has aring-shaped wall part 42 a firmly contacting a side surface 41 b of thefirst half 41. A part extending from one side of the ring-shaped wallpart 42 a close to the propeller is a small diameter tube part 42 b forbeing fitted in a hole 33 b formed in the side end wall 33 a of the boss33 of the propeller 31 and being spaced by a distance S from thepropeller shaft 30. A part extending from the other side of thering-shaped wall part 42 a is a large diameter tube part 42 c for beingfitted to an outer peripheral surface 41 c positioned outside the taperhole 41 a of the first half 41.

The propeller shaft 30 and the propeller 31 are preferably made ofstainless steel. It is preferable that the first half 41 and the secondhalf 42 are made of brass and plated with hard chromium.

Next, an effect of this preferred embodiment will be described usingFIG. 2.

In the case that the hull or the stern comes to the surface, a draftline lowers, and an upper part of the propeller 31 is exposed to the airwhen the propeller is rotating, a water resistance force acts upward ona lower part of the propeller 31. The water resistance force actingupward on the lower part of the propeller 31 becomes the largesttogether with a thrust force when the watercraft is driven at a highspeed, and acts on the propeller shaft 30.

In the above construction, a side surface of a side end wall 33 a of theboss 33 of the propeller 31 firmly contacts a side surface of thering-shaped wall part 42 a of the second half 42. A side surface on theopposite side of the ring-shaped wall part 42 a of the second half 42firmly contacts a side surface of the side surface part 41 b of thefirst half 41. The surfaces of the taper hole 41 a of the first half 41and the taper part 30 b of the propeller shaft 30 are contra-positive toeach other. Therefore, a thrust force acting on the propeller 31 istransmitted from the side surface of the side end wall 33 a of the boss33 of the propeller 31 to the side surface of the ring-shaped wall part42 a of the second half 42. Then, the thrust force is transmitted fromthe side surface on the opposite side of the ring-shaped wall part 42 aof the second half 42 to the side surface of the side surface part 41 bof the first half 41, and next transmitted from the taper hole 41 a ofthe first half 41 to the taper part 30 b of the propeller shaft 30.

In the above construction, if the spacer 40 is formed into one body asin a conventional case shown in FIG. 3, a moment acts on a point ofapplication of an average thrust on a thrust force transmission surfacedue to an upward force acting upward on the small diameter tube part.However, in this preferred embodiment, the spacer 40 is divided into thefirst half 41 and the second half 42. The large diameter tube part 42 cof the second half 42 is fitted to the outer peripheral surfacepositioned outside the taper hole 41 a of the first half 41, and thereis the space S between the small diameter tube part 42 b and the outershaft part 30 a of the propeller shaft 30. Therefore, a water resistanceforce F acting upward on the lower part of the propeller 31 acts upwardon the small diameter tube part 42 b of the second part 42, and istransmitted from the large diameter tube part 42 c to the outerperipheral surface positioned outside the taper hole 41 a of the firsthalf 41. This force is then transmitted from the taper hole 41 of thefirst half 41 to the taper part 30 b of the propeller shaft 30. Thereby,a water resistance force F acting upward on the lower part of thepropeller 31 mentioned above acts on a position almost corresponding toa point of application of an average thrust on a thrust forcetransmission surface between the taper hole 41 a of the first half 41and the taper part 30 b of the propeller shaft 30.

With the propeller thrust transmission device of this preferredembodiment, a point of application of a water resistance force actingupward on the lower part of the propeller 31 almost corresponds to apoint of application of an average thrust on the thrust forcetransmission surface between the taper hole 41 a of the first half 41and the taper part 30 b of the propeller shaft 30, and thus a momenteffect due to a water resistance force acting upward on the lower partof the propeller 31 almost does not occur. Therefore, the occurrence ofa precession of the surface of the taper hole 41 a of the first half 41around an entire circumference of the taper part 30 b of the propellershaft 30 is prevented, and an abrasion on the thrust transmissionsurface by the first half 41 of the spacer 40 can be prevented. Further,the spacer 40 is divided into the first half 41 and the second half 42,and thus a position in which an upward force acting on the propeller 31is transmitted to the propeller shaft 30 is changed. Therefore, areshape of the propeller 31 or the gear case 26 is not necessary, and anapplication to a product that has already been shipped and sold can befacilitated.

In this preferred embodiment, the firm contacting surface between theside surface of the first half 41 and the ring-shaped wall part of thesecond half 42 corresponds to a small diameter end of the taper part 30b of the propeller shaft 30. With this construction, a ring-shaped sidewall 42 a of a second half 42 can be formed to have a thickness with aminimum necessary strength. This allows the taper hole 41 a of the firsthalf 41 to be contra-positive to a surface of the taper part 30 b of thepropeller shaft 30 over an entire length of the taper part 30 b, andthereby, the occurrence of a moment effect is inhibited. A thrust forceper unit area becomes smaller because an area receiving a thrust forcebecomes larger than a conventional case, and a force acting upward onthe propeller 31 per unit area becomes small also. Therefore, it canmore effectively prevent an occurrence of a precession of the surface ofthe taper hole 41 a of the first half 41 around the entire circumferenceof the taper part 30 b of the propeller shaft 30.

In this preferred embodiment, the small diameter tube part 42 b isforcedly fitted in a hole 33 b formed in the side end wall 33 a of theattachment part 33 of the propeller 31. Consequently, the second half 42which is a part of the spacer 40 is practically united with the boss 33of the propeller 31 because of a length of the forced fitting in anaxial direction. Therefore, a water resistance force F acting upward onthe lower part of the propeller 31 is certainly transmitted from thelarge diameter tube part 42 c of the second half 42 to the outerperipheral surface positioned outside the taper hole 41 a of the firsthalf 41, and acts on a position almost corresponding to a point ofapplication of an average thrust on the thrust force transmissionsurface between the taper hole 41 a of the first half 41 and the taperpart 30 b of the propeller shaft 30. The large diameter tube part 42 cis fitted in the outer peripheral surface positioned outside the taperhole 41 a of the first half 41 to have a loose fit tolerance, and thus,it prevents an occurrence of a precession on a fitting surface.

FIG. 3 is a cross sectional view of the propeller thrust transmissiondevice for a watercraft propulsion device according to a secondpreferred embodiment of the present invention. The propeller thrusttransmission device includes a concentricity retaining ring 37 at an endpart of the bush 35 close to the lower case 26, and thereby theconcentricity between the boss 33 and the bush 35 is retained at the endof the bush 35 close to the lower case 26 if the rubber damper 34between the boss 33 and the bush 35 elastically deforms and flexes.Other parts of construction are preferably the same as the firstpreferred embodiment.

More specifically, in this propeller thrust transmission device, theattachment part 32 of the propeller 31 is furnished with the boss 33united with the impeller part of the propeller 31 and having an exhaustpassage for combustion gas of the engine, the bush 35 positioned in theboss 33 and is spline-fitted to the propeller shaft 30, the rubberdamper 34 press-fitted in a tube-shaped space between the boss 33 andthe bush 35, and the endplate 36 for closing the bush 35 and the rubberdamper 34 in. In addition, the attachment part 32 is furnished with theconcentricity retaining ring 37 for retaining the concentricity betweenthe bush 35 and the boss 33, which is forcedly fitted in an end of thebush 35 close to the gear case and fills a space between the bush 35 andthe boss 33 with a loose fit tolerance to the boss 33. The attachmentpart 32 is clamped down and fixed to a screw part at an end of thepropeller shaft 30 by a nut 38.

With this construction, although the concentricity between the boss 33and the bush 35 as a whole is retained via the rubber damper 34, theconcentricity is retained with the concentricity retaining ring 37 at apart close to the gear case if the rubber damper 34 flexes. That is, inthe case that the hull or the stern comes to the surface, a draft linelowers, and the upper part of the propeller is exposed to the air whenthe watercraft propels at a high speed (when the propeller rotates at ahigh speed), a water resistance force F acts upward on the lower part ofthe propeller. In this situation, a lower part of the rubber damper 34is compressed. It causes a state that the boss 33 moves up toward thebush 35. However, the state that the boss moves up toward the bush isprevented at the part close to the gear case. As a result, a slidingmovement of the side end wall of the boss 33 on the end surface of thespacer is prevented, and thereby an occurrence of abrasion between theside end wall 33 a of the boss 33 and the end surface of the second half42 is prevented, and further, an occurrence of abrasion between thesecond half 42 and the end surface of the first half 41 is prevented.Therefore, an occurrence of abrasion on the thrust transmission surface(the taper part) of the propeller shaft 30 by the first half 41 isprevented.

In each of the above preferred embodiments, the outboard motor 21 ispreferably used as the “watercraft propulsion device.” However, thepresent invention is not limited to this, and the outboard motor 21 maybe replaced by an inboard/outboard motor. It is only required that thefitting between the hole 33 b of the boss 33 of the propeller 31 and thesmall diameter tube part 42 b of the second half 42, and the fittingbetween the large diameter tube part 42 c of the second half 42 and theouter periphery part of the first half 41 provide a steady bond betweena shaft and a hole without wobbling. The concentricity retaining ring 37should be forcedly fitted in either one of the boss or the bush andfitted in the other with a loose fit tolerance.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A propeller thrust transmission device for a watercraft propulsiondevice, comprising: a taper part provided at a position close to a gearcase on an outer shaft part, in which a propeller attachment part isfitted in and fixed at the outer shaft part protruding outward from thegear case of a propeller shaft, a diameter of an end of the taper partlocated close to the gear case is large and a diameter of an end of thetaper part located close to a propeller is small; and a spacer includinga taper hole whose surface is contra-positive to the taper part and inwhich the taper part is fitted, the spacer including: an end surfacearranged to contact a side end wall of the propeller attachment part; asmall diameter tube part fitted in a hole formed in the side end wall ofthe propeller attachment part such that a thrust force acting on thepropeller when the propeller rotates in its normal direction is receivedby the taper part of the propeller shaft via the spacer; a first half;and a second half separate from the first half; wherein the first halfincludes the taper hole whose surface is contra-positive to the taperpart and in which the taper part is fitted; and the second half islocated closer to the propeller relative to the first half and has aring-shaped wall part firmly contacting a side surface of the firsthalf, a part extending from one side of the ring-shaped wall part closeto the propeller is the small diameter tube part fitted in the holeformed in the side end wall of the propeller attachment part and spacedfrom the propeller shaft, and a part extending from the other side ofthe ring-shaped wall part has a large diameter tube part fitted in anouter peripheral surface positioned outside the taper hole.
 2. Thepropeller thrust transmission device for a watercraft propulsion deviceaccording to claim 1, wherein a contacting surface between the sidesurface of the first half and the ring-shaped wall part of the secondhalf corresponds to a small diameter end of the taper part of thepropeller shaft.
 3. The propeller thrust transmission device for awatercraft propulsion device according to claim 1, wherein the smalldiameter tube part is forcedly fitted in the hole formed in the side endwall of the propeller attachment part.
 4. The propeller thrusttransmission device for a watercraft propulsion device according toclaim 1, wherein the propeller attachment part includes a boss unitedwith an impeller part of the propeller, a bush mounted inside the bossin which the propeller shaft is fitted, an elastically deformable dampermember provided between the boss and the bush, and a concentricityretaining ring provided on an end part of the bush close to the gearcase so as to fill a space between the bush and the boss and so as toretain the concentricity between the bush and the boss, and is fixed tothe propeller shaft by a nut.